Comment by vee-kay

Fun trivia: XLSX, DOCX, PPTX are just XML files, you can rename them to ".XML" file extension, and open them in notepad to see their raw contents.

But you can use qpdf or PDFEdit to interpret a PDF's raw code.

https://stackoverflow.com/a/6562443

And thus, you can compare the raw XLSX (XML) vs raw PDF.